Vehicle air suspension

ABSTRACT

The invention is an air suspension system on vehicle driven axle to maintain substantially constant pinion shaft angle in response to traction force reaction on axle and brake torque induced reaction on axle and in response to position of axle in jounce and rebound. The invention is based on four bar mechanism geometrically arranged to achieve substantially constant pinion shaft angle. The four bars are represented by 1) hanger bracket, 2) trailing arm, 3) link rod and 4) driven axle housing with its attachments. In one of the preferred embodiments, the trailing arm is pivotally connected to top portion of hanger bracket attached to frame rail. The middle portion of trailing arm is “spherically” connected to axle top. Rear portion of trailing arm is connected to frame rail by air spring and shock absorber. One end of said link rod is pivotally connected to lower portion of hanger bracket and other end is pivotally connected to lower portion of axle.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to vehicle trailing arm air suspension system, more particularly to a driven axle and more relevant to tandem driven axles. Driven axles of trucks carry invariably an input shaft also called pinion shaft to which is connected a propeller shaft to transmit power from engine to the differential assembly from where power is distributed to the wheels. A cardan type universal joint generally joins the propeller shaft and pinion shaft in the driven axle. Angle of pinion shaft is set in a truck to achieve low included angle between the propeller shaft and pinion shaft. Low included angle between the propeller shaft and the pinion shaft will induce low torsional acceleration of the pinion shaft which is desirable. Maintaining the pinion shaft angle around its set design angle in various positions of the axle travel during jounce and rebound is a challenge in a trailing arm air suspension. Change in the pinion angle from its ideal design angle will increase driveline induced vibrations to the suspended mass of the vehicle and also reduce the life of the driveline components including cardan joint. A substantially constant pinion shaft angle maintained around the ideal design angle would result in low cardan joint induced vibrations and longer life of parts in the driveline, including transmission parts.

During vehicle acceleration, deceleration, and braking, the axle is subjected to equal and opposite reactions in response to drive torque and braking torque. Torsional resilience, about the axle lateral axis, is generally incorporated in the suspension systems. In a suspension where the trailing arm is “rigidly” connected to the axle, due to this suspension torsional resilience, the reaction torque on axle changes the pinion shaft angle unless this reaction torque is suitably countered.

2) Description of the Related Art

2.1) Single Driven Axle Suspension:

A typical truck trailing arm air suspension functionally attached to a driven axle has a pair of trailing arm assemblies, comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers. The front end of trailing arm of each assembly is pivotally connected to or longitudinally sliding in hanger brackets. The later is aided by additional tie link between axle and hanger bracket. The middle portion of trailing arm is generally “rigidly” connected to one side of axle housing. The trailing arm generally extends behind the axle where it is connected to an air spring and to a shock absorber. The front portion of trailing arm bears partial suspended weight of the vehicle. The rear portion of the trailing arm bears partial suspended weight through the air spring which is connected to the frame rail. The rigid attachment of the trailing arms to axle combined with pivoted or vertically restrained sliding of the front end of the trailing arm to the hanger bracket, make the suspension inherently reactive to torque induced by traction force and wheel braking torque. Due to the resilience in the suspension system, this reaction changes pinion shaft angle of the driven axle. The effect is more pronounced during vehicle acceleration from stop and during vehicle hard braking. While it is a industry practice to set the pinion angle to its ideal design angle that cancels the joint-working-angle of all the cardan joints in the driveline system, a ‘rigidly axle mounted trailing arm set up’ generally does not maintain the pinion shaft angle during jounce and rebound of axle and during acceleration and braking.

Therefore in a driven axle, it is desirable to have pinion shaft angle closer to its ideal design angle during any condition of power transmission from engine to wheels and wheels to engine and during jounce and rebound motion of axle.

2.2) Tandem Driven Axle Suspension:

Typical trailing arm air suspension of tandem driven axles has two pairs of trailing arm assemblies, each comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers on each axle. The front end of trailing arm of each assembly is pivotally connected to or longitudinally sliding in hanger brackets. The later aided by additional tie link between axle and hanger bracket. The middle portion of trailing arm is generally “rigidly” connected to housing of driven axle. The front portion of trailing arm bears partial suspended weight. Rear portion of trailing arms bear partial suspended weight through air springs. Drive torque is transmitted from front driven axle to rear driven axle through an inter-axle propeller shaft. Output shaft of front driven axle is connected to the inter axle propeller shaft generally by a cardan type universal joint. Other end of inter-axle propeller shaft is connected to the pinion shaft of the rear driven axle generally by another cardan type universal joint. Depending on the geometric configuration of the tandem axles, the pinion shaft angles are set to their ideal design angle to achieve near equal and low included joint angles between the pinion shafts and the inter axle propeller shaft. Angle of the pinion shafts change during drive torque transmission to the pinion shafts of the axles and during vehicle braking due to the torsional resilience (about the axle lateral axis) of the suspension. Angle of the pinion shafts change during jounce and rebound of axles, increasing or decreasing the included joint angles between the pinion shafts and the inter-axle propeller shaft. Both parallel pinion arrangement and broken back arrangement of the pinion shafts are susceptible to change in pinion shaft angle from their ideal design angle. Effect of this change is higher torsional and inertial vibrations emanating from the inter axle shaft joints of both axles causing occupant discomfort and cumulative structural damage to the driveline parts.

One of the advantages of prior art “rigidly” axle mounted trailing arm air suspensions is their simple construction for the application that the suspensions are intended. Prior art rigidly mounted trailing arm air suspensions are more suitable for low torque engines in the range of 1050 ft.lb to 1650 ft.lb wherein the effect of reactive torque on driven axle is lesser. However, pinion shaft angle change during jounce and rebound still exist in these “rigidly” axle mounted air suspensions.

With higher torque output of current generation engines and higher braking performance demands for similar applications, maintaining the pinion shaft angles close to their ideal design angle during vehicle operation has become more challenging with prior art “rigidly” axle mounted trailing arm air suspensions.

SUMMARY OF THE INVENTION

The invention is a vehicle trailing arm air suspension system and more particularly a truck driven-axle air suspension system. One of the preferred embodiment of this invention is based on four bar mechanism, the four bars represented by 1) hanger bracket, 2) trailing arm of preferably spring steel and preferably rectangular cross section, 3) link rod and 4) driven axle housing with its attachments. The invention as applied to a single driven axle comprises a pair of trailing arm assemblies. Each assembly comprises a hanger bracket, a trailing arm and its attachments to hanger bracket and axle, a link rod and its attachments to hanger bracket and axle, an air spring and shock absorber. Front end of the trailing arm is pivotally connected to upper portion of hanger bracket. The hanger bracket is rigidly attached to the frame rail. The middle portion of the trailing arm is “spherically” connected to top of driven-axle by two concentric spherical segments one below and one above the trailing arm. The spherical segments are suitably keyed to the trailing arm to prevent linear relative movements between the segments and the trailing arm. The spherical segments are preferably fastened together on either sides of the trailing arm. The said spherical segments are contained and slide inside matching spherical cavities formed in blocks above and below trailing arm. The said blocks together are rigidly attached to top of the axle by clamping them to the axle preferably using U-shaped bolts. All four spherical surfaces have a common center. Required clearance is maintained between the spherical cavities in the blocks and the spherical segments to allow free sliding of the spherical surfaces of segments on the matching spherical surfaces of blocks. The spherical segments combined with spherical cavities in the blocks form a limited articulation spherical joint. The center of the joint thus formed by the spherical surfaces of segments and blocks act as one of four nodes of four bar mechanism. The pivoted connection of the front end of the trailing arm acts as one of four nodes. The portion of the trailing arm, rear of axle, is connected to the bottom of an air spring and to bottom of a shock absorber. Other end of the air spring and the shock absorber are connected to the main frame rail. One end of the link rod is pivotally connected to the lower portion of hanger bracket and other end is pivotally connected to the lower portion of the axle to form one of the links of four bar mechanism. In operation, the hanger bracket acts as the ‘ground link’ of the four bar mechanism and driven axle, with its connections to trailing arm and link rod, acts as the ‘driven link’ of four bar mechanism. This arrangement of four bar mechanism thus formed is geometrically arranged to achieve the required ideal design angle of the pinion shaft. The lengths of opposite links are preferably maintained equal to achieve substantially constant pinion shaft angle during jounce and rebound motion of axle. This arrangement of four bar mechanism makes the suspension substantially non-reactive to traction force reaction and brake torque reaction on axle. Drive torque and brake torque induced reaction on axle, about axle axis, are substantially countered by the front portion of the trailing arm and the bottom link rod. To control the lateral motion of the axle during jounce and rebound, one end of a tie rod is pivotally or spherically attached to the frame rail and the other end of the tie rod is pivotally or spherically attached to the axle. The vertically resilient front portion of the trailing arm and the air spring in the rear portion of trailing arm act as energy absorption elements of the suspension. Though the preferred embodiment of this invention has a vertically resilient front portion of the trailing arm, it can also be a non-resilient trailing arm. The spherical joint on top of the axle substantially relieves the axle of forces that may otherwise strain the axle if the trailing arm is rigidly attached to axle, more particularly during cross articulation when the wheels on either side of the axle are not in same horizontal plane.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1 is the general view of the invention pertaining to a single driven axle as shown assembled on a truck frame rail assembly.

FIG. 2 is the general view of the invention pertaining to a single driven axle (without tires) as shown assembled on a truck frame rail assembly.

FIG. 3 is the view of the invention pertaining to a single driven axle viewed from left side.

FIG. 4 is the longitudinal vertical section of the invention through the center of the spherical joint.

FIG. 5 is the general view of the invention for a tandem driven axle as seen assembled on a truck frame rail.

FIG. 6 is the general view of the invention for a tandem driven axle as seen assembled on a truck frame rail without the tires.

FIG. 7 is the left side view of the invention for a tandem driven axle, with axle and inter axle propeller shaft.

FIG. 8 through 13 shows the various embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates portion of the truck chassis showing the general arrangement of the suspension on a single driven axle with the propeller shaft 101 and axle 150. Frame rails 03 and 04 are oppositely spaced steel channel sections oriented longitudinally in the truck. Hanger brackets 05 and 06 are shown mounted on the out-board side of the frame rails. Tires 08 are shown mounted on either side of the axle 150. Partial view of propeller shaft 101 is shown connected by cardan type universal joint 102 to a driven axle 150.

FIG. 2 illustrates portion of truck chassis showing general arrangement of the suspension on a single driven axle without tires. The hanger brackets 05 and 06 are rigidly attached to the frame rails 03 and 04 respectively by a plurality of fasteners. Trailing arms 09 and 10 are shown connected to the upper portion of the hanger brackets 05 and 06 by pivot pins 11 (not visible in the Figure) and 12 respectively. The portion of the trailing arms 09 and 10 ahead of axle 150 up to the pivot pins 11 or 12 is referred to as the front portion of the trailing arms. One end of link rods 13 and 14 are connected to the lower portion of the hanger brackets 05 and 06 by pivot pins 15 and 16 respectively. Other end of the link rods 13 and 14 are pivotally connected to bottom brackets 17 and 18 using pins 27 and 28. The bottom brackets 17 and 18 are rigidly attached to lower portion of axle 150 by U-bolts 19, 20 21 and 22. The rear portion of the trailing arms 09 and 10 is attached to bottom of air springs 23 and 24 and shock absorbers 25 and 26. The top of the air springs 23 and 24 and shock absorbers 25 and 26 are attached to the frame rails 3 and 4 by suitable bracketry and fasteners.

FIG. 3 illustrates the side view of the general arrangement of the invention. The components are numbered such that the odd numbers represent those parts belonging to the right hand side trailing arm assembly and the even numbers represent the parts belonging to the left hand side trailing arm assembly with the exception of axle 150 and cardan joint 102. This illustration need to be correlated with FIG. 4 for clarity.

FIG. 4 illustrates attachment of the middle portion of the trailing arm 10 to the top of axle 150 by an assembly of blocks and spherical segments. For the purpose of clarity, only left side trailing arm assembly is explained. The figure shows partial section of the trailing arm assembly. In the illustration, spherical segment-top 30 and spherical segment-bottom 32 which have integral cylindrical projections are shown inserted in matching depressions in trailing arm 10. The spherical surface of segment-top 30 engages with the matching spherical surface in the block-top 34. Similarly, the spherical surface in the segment-bottom 32 engages with the spherical surface in the block-bottom 36. Suitable spherical shapes of bushing material interface between the segments and blocks. All spherical surfaces in the assembly are arranged to have a common center point. This ensures the assembly acts as a single spherical joint. The figure also illustrates the four bar links. The distance between pin 12 and pin 16 represents ground link L1 of the four bar mechanism. The distance between pin 16 and pin 28 represents the second link L2. Distance between pin 28 and the center formed by the spherical joint on top of the axle represents the driven link L3 of the four bar mechanism. The mechanism is completed by the link L4 formed between the spherical joint and pin 12.

FIG. 5 illustrates portion of the truck chassis showing the general arrangement of the invention on tandem driven axles.

FIG. 6 illustrates portion of truck chassis showing general arrangement of the suspension on tandem driven axles without tires. Since the suspension in these axles are akin to that of single driven axle, the definitions and assembly arrangements are common to single driven axle suspension explained above.

FIG. 7 illustrates the side view showing general arrangement of the suspension on tandem driven axles.

FIG. 8 shows one of the preferred embodiments of the invention. In this embodiment, the spherical joint center is above the ‘axle housing section’.

FIG. 9 shows another embodiment of the invention where the said spherical joint center is below the ‘axle housing section’.

FIG. 10 shows another embodiment of the invention where the said spherical joint center is above the ‘axle housing section’ and the center of the said spherical joint is above the trailing arm.

FIG. 11 shows another embodiment of the invention where the said spherical joint center is below the ‘axle housing section’ and the center of the spherical joint is above the trailing arm.

FIG. 12 shows another embodiment of the invention where the said spherical joint is formed by 1) segment-top, 2) a spherical ball, 3) block-top, 4) segment-bottom and 5) block-bottom. The spherical joint center is above the axle housing section and the center of the said spherical joint is above the trailing arm.

FIG. 13 shows another embodiment of the invention where the said spherical joint is formed by 1) segment-top, 2) a spherical ball, 3) block-top, 4) segment-bottom and 5) block-bottom. The spherical joint center is below the axle housing section and the center of the said spherical joint is above the trailing arm.

Features of the Spherical Joint Trailing Arm Four Bar Mechanism Air Suspension:

The invention is capable of supporting high torque engines more suitably in the range of 1650 ft lb. to 2250 ft lb. Based on the structural capacity of the components in the suspension, engine torque capacity can be higher.

When used on a 4×2, 6×4, 8×6 (tridem) wheel configuration of a tractor, the invention can substantially cancel cardan joint working angle as explained in the summary of the invention.

When used on a 6×2 configuration of a truck, the invention can substantially cancel cardan joint working angle on driven axle as explained in the summary of the invention and can be, by suitable mechanism, made to lift the rear non-driven axle when the truck is partially loaded or unloaded to reduce fuel consumption and increase tire life.

Due to substantial cancellation of reaction induced by traction force on the driven axle, the frame raise that is inherent in “rigidly” axle mounted trailing arm air suspension is substantially reduced by this invention.

Due to substantial cancellation of reaction induced by braking force on the driven axle, the frame squat that is inherent in “rigidly” axle mounted trailing arm air suspension is substantially reduced by this invention.

Although the above description relates to specific preferred embodiments as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein. 

1. A trailing arm air suspension assembly for bearing partial weight of vehicle comprising: a trailing arm featuring leading portion, middle portion and trailing portion; the said leading portion of the said trailing arm is formed to be vertically resilient or non-resilient; said trailing portion of the said trailing arm adapted to be connected to air spring and a shock absorber either directly or through an adaptor; said middle portion of the said trailing arm adapted to mate with the parts that form a spherical joint; a hanger bracket adapted to be rigidly connected to the vehicle frame rail and adapted to pivotally connect the front end of the trailing arm and one end of a link rod; an axle adapted to connect parts which form the spherical joint and adapted to connect parts which interface the other end of the said link rod with the axle.
 2. A suspension of claim 1 wherein the front end of the said trailing arm is pivotally connected to said hanger bracket by a cylindrical pin or with compliant rubber bushing.
 3. A suspension of claim 2 wherein the said middle portion of the said trailing arm is connected to spherical segments below and above the said trailing arm.
 4. A suspension of claim 3 wherein the said spherical segments are contained in matching spherical cavities or spherical projections in the spherical blocks above and below the said trailing arm.
 5. A suspension of claim 4 wherein a spherical ball is used between the said spherical segments and the said spherical blocks as an alternative arrangement.
 6. A suspension of claim 5 wherein bearing bushings interface between the spherical surfaces of said spherical segments and said spherical blocks or said spherical ball.
 7. A suspension of claim 6 wherein the said spherical blocks are rigidly connected to the axle by U shaped bolts or straight bolts intended to prevent relative movements between the axle housing and the spherical joint assembly formed by the said spherical segments and said spherical blocks.
 8. A suspension of claim 7 wherein the middle portion of the trailing arm articulates about the center of the said spherical joint formed by the said spherical segments and said spherical blocks.
 9. A suspension of claim 8 wherein there is provided a bracket rigidly attached to the said axle for connecting one end of the link rod to the axle, opposite to the side of the said spherical joint with regard to the axle axis.
 10. A suspension of claim 9 wherein said link rod is pivotally connected to the said axle bracket by a cylindrical pin or with compliant rubber bushing for connecting one end of the said link rod to the axle assembly.
 11. A suspension of claim 10 wherein the other end of the said link rod is pivotally connected by a cylindrical pin or with compliant rubber bushing to the said hanger bracket.
 12. A suspension of claim 11 wherein the assembly comprising the said trailing arm, said spherical segments, said spherical blocks, said U-shaped bolts, said bracket for connecting the said link rod to the axle, said hanger bracket and said pins are geometrically arranged to form a four bar mechanism.
 13. A suspension of claim 12 wherein the said spherical joint is formed below or above said axle section.
 14. A suspension of claim 13 wherein the center of the said spherical joint is below or above or within the thickness of the said trailing arm.
 15. A suspension of claim 14 wherein an air spring is connected to the said trailing portion of the said trailing arm either directly to the said trailing arm or through an adapter.
 16. A suspension of claim 15 wherein the other end of the said air spring is connected to the said frame rail of the vehicle.
 17. A suspension of claim 16 wherein one end of a shock absorber is connected to the suspension assembly and the other end of the shock absorber is connected to the said frame rail either directly or through an adaptor.
 18. The suspension of claim 17 wherein a pair of said trailing arm assemblies connected to either side of driven axle assembly and connected to the frame rails form a vehicle suspension system wherein the driven axle angle is maintained substantially constant in any vertical position of the said driven axle.
 19. The suspension assembly of claim 18 wherein the said axle is laterally controlled in its lateral travel by a tie rod spherically or pivotally connecting one of the said frame rail and the said axle. 